In the field of noninvasive ventilation, for example as described in U.S. Pat. No. 6,532,957, a problem arises particularly in patients newly introduced to servoventilation. The patient's arterial CO2 partial pressure (PCO2) may be well above the value preferred by the clinician; for example, the PCO2 may be 60 mm Hg, and the clinician would prefer to stabilize it at 45 mm Hg. This would require the patient's alveolar ventilation to be increased by a factor of approximately 60/45=4/3. Yet if the clinician sets the target ventilation of the servoventilator to 4/3 of the patient's current ventilation, such a large increase in ventilation, if it occurs immediately, is likely to abolish all respiratory drive and much of the upper airway drive (leading to problems with upper airway obstruction). It may cause glottic closure, preventing the ventilation from increasing to the target level, despite the ventilator delivering the maximum level of pressure support for which it is programmed, which may lead to arousal from sleep. If the arterial pH is relatively normal at the beginning of therapy, indicating a metabolic compensation for a relatively chronic respiratory acidosis, a sudden large increase in ventilation would result in a marked alkalosis, with undesirable electrolyte shifts, including hypokalaemia, with the potential for inducing cardiac arrhythmias.
For these reasons a progressive increase of target ventilation over a period of time, typically several days or weeks, is desirable. This might be achieved by frequent manual changes of the target ventilation, but this would be inconvenient, since the patient is likely to be at home at this stage.